Apparatus for and method of controlling internal combustion engine

ABSTRACT

Under a partial load, a pumping loss is reduced by a stratified combustion to enhance a fuel consumption, and during the maximum output operation, the output is increased by a premixture combustion, and the output of an engine is controlled, thereby enhancing the drivability. Under the partial load, an ignition source is provided in the vicinity of a fuel injection valve, and after the fuel is injected, the mixture is ignited, and a resulting flame is caused by a spray of the fuel to spread into a cylinder, thereby effecting a stratified combustion. When the load increases, so that soot and so on are produced in the stratified combustion, the fuel injection is effected a plurality of times in a divided manner, and a premixture is produced within the cylinder by the front-half injection, and a flame, produced by the latter-half injection, is injected into the cylinder to burn this premixture.

This application is a continuation of application Ser. No. 10/057,922(now U.S. Pat. No. 6,453,871), filed Jan. 29, 2002 which is acontinuation of application Ser. No. 09/709,404, filed Nov. 13, 2000(now U.S. Pat. No. 6,343,585), which is a continuation of applicationSer. No. 09/549,180, filed on Apr. 13, 2000 (now abandoned), which is acontinuation of application Ser. No. 09/236,321, filed on Jan. 25, 1999(now U.S. Pat. No. 6,148,791), which is a continuation of applicationSer. No. 08/850,012, filed May 1, 1997 (now U.S. Pat. No. 5,875,761),which, in turn, is a divisional of application Ser. No. 08/362,878,filed Dec. 23, 1994 (now U.S. Pat. No. 5,666,916), the entiredisclosures of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a spark-ignition internal combustionengine, and more particularly to an apparatus for and a method ofcontrolling a spark-ignition internal combustion engine of the type inwhich fuel is injected directly into a cylinder.

2. Related Art

There is known a conventional system (Japanese Patent UnexaminedPublication No. 2-153257) in which fuel is injected directly into acylinder by use of the air pressure. A conventional diesel engineutilizes a stratified combustion, and therefore the maximum output orpower is low although the fuel consumption under a partial load isenhanced. On the other hand, a conventional gasoline engine has adrawback that although the maximum output or power is high because of apremixture combustion, the fuel consumption under a partial load isworsened because of a pumping loss.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an apparatus for and amethod of controlling an internal combustion engine, in which under apartial load, a pumping loss is eliminated by a stratified combustion,thereby enhancing the fuel consumption, and during a maximum-outputoperation, the output or power is increased by a premixture combustion,and an engine torque is controlled to improve the operability(drivability), the fuel consumption and an exhaust cleaning effect.

In order to overcome the above problem of the prior art, under a partialload, an ignition source is provided in the vicinity of a fuel injectionvalve, and after the fuel is injected, the mixture is ignited, and aresulting flame is caused by a spray of the fuel to spread into acylinder, thereby effecting a stratified combustion. On the other hand,when the load increases, so that soot and so on are produced in thestratified combustion, the fuel injection is effected a plurality oftimes in a divided manner, and a premixture is produced within thecylinder by the former-half injection, and a flame, produced by thelatter-half injection, is injected into the cylinder to burn thispremixture. Thus, the premixture is burned in a short period of time.When changing the gear ratio of a transmission, the amount of the fuelis changed so that a step will not develop in a torque.

When the amount of injection of the fuel is small as in a partial-loadoperation, the initiation of the injection and the ignition timing canbe relatively close to each other, and therefore the fuel is not so muchspread within the cylinder, and the combustion (stratified combustion)takes place in a relatively narrow range. In accordance with theincrease of the load, the initiation of the injection is made earlier,so that the range of formation of the mixture (premixture) increases,and a premixture combustion takes place, thereby increasing the producedtorque.

In accordance with the drive torque, the gear ratio of the transmissionis selected, and if the drive torque need to be further increased, thegear ratio of the transmission is increased. When changing the gearratio, the fuel injection amount is controlled so that the drive torquewill not be varied. The fuel is injected into the combustion chamber ofthe engine by a fuel injection valve having a port (opening) therein,and therefore the fuel will not deposit on an intake manifold and otherportions, and the speed of inflow of the fuel is high, and the enginetorque can be controlled with a good response. The air/fuel ratio can beset to a large value, and therefore a throttle valve opening degree canbe increased to reduce a pumping loss, thereby enhancing a fuelconsumption. Moreover, since the air/fuel ratio can be increased, theamount of CO and HC in the exhaust gas can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a control system according to a first embodiment ofthe present invention;

FIG. 2 is a vertical cross-sectional view of a combustion chamber;

FIG. 3 is a diagram showing the correlation between the air/fuel ratioA/F and HC in exhaust gas, as well as the relation between A/F and NOxin the exhaust gas;

FIG. 4 is a vertical cross-sectional view of a combustion chamber as inFIG. 2, but showing a second embodiment of the invention;

FIG. 5 is a chart showing a fuel injection timing;

FIG. 6 is a flow chart for the calculation of a fuel injection time;

FIG. 7 is a block diagram of a fuel pressure control device;

FIG. 8 is a view showing an EGR control system;

FIG. 9 is a diagram showing the construction of a control systemaccording to a third embodiment of the invention;

FIG. 10 is a time chart showing the operation of an intake valve;

FIG. 11 is a perspective view showing rocker arms;

FIG. 12 is a map diagram for selecting a cam in connection with therelation between an engine speed and an accelerator opening degree;

FIG. 13 is a map diagram for selecting a cam in connection with therelation between the engine speed and an engine torque;

FIG. 14 is a diagram showing the correlation between the air/fuel ratioA/F and the engine torque;

FIG. 15 is a diagram showing the correlation between the fuel amount andthe engine torque;

FIG. 16 is a block diagram of a control system according to a fourthembodiment of the invention;

FIG. 17 is a block diagram of a control system according to a fifthembodiment of the invention;

FIG. 18 is a map diagram showing the relation between the targetair/fuel ratio and the engine torque;

FIG. 19 is a diagram showing the correlation of a throttle valve openingdegree with the engine speed and the intake air amount;

FIG. 20 is a block diagram of a control system according to a sixthembodiment of the invention;

FIG. 21 is a block diagram of the control system, according to anembodiment of the invention, similar to the system of FIG. 20;

FIG. 22 is a top plan view showing the construction of a cylinder gasketof an engine in a seventh embodiment of the invention;

FIG. 23 is a vertical cross-sectional view of the construction of FIG.22;

FIG. 24 is a view showing another embodiment of the invention;

FIG. 25 is a diagram showing the correlation between a required torqueand an engine torque;

FIG. 26 is a diagram showing the correlation between a throttle valveopening degree and the required torque;

FIG. 27 is a diagram showing the correlation between the required drivetorque and the gear position;

FIG. 28 is a diagram showing the correlation between a vehicle speed andthe engine torque;

FIG. 29 is a flow chart for the control of a transmission and theengine;

FIG. 30 is a diagram showing the correlation between an acceleratoropening degree and the required drive torque;

FIG. 31 is a diagram showing the correlation between the acceleratoropening degree and the vehicle speed;

FIG. 32 is a diagram showing the correlation between the engine speedand the engine torque;

FIG. 33 is a diagram showing the correlation between the engine speedand the engine torque;

FIG. 34 is a time chart showing the change of the engine torque and thethrottle valve opening degree with time;

FIG. 35 is a control block diagram of still another embodiment of theinvention;

FIG. 36 is a time chart showing the change of the fuel amount and thevehicle acceleration with time; and

FIG. 37 is a time chart showing the change of the air amount, the fuelamount and the vehicle acceleration with time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the construction of a control system according to a firstembodiment of the invention. Fuel is fed from a fuel tank 1 to a fuelpump 2, and the fuel is pressurized by this pump 2. A pressure sensor 3detects the pressure of the pressurized fuel, and feeds a pressuresignal to a control circuit 5. The control circuit 5 compares the fuelpressure with a predetermined target value, and if the fuel pressure ishigher than this predetermined value, a spill valve 4 of the fuel pump 2is opened to control the fuel pressure to the target pressure. Thepressurized fuel is fed to a fuel injection valve 13. A signal (torquesignal) intended by the driver is fed from an accelerator pedal 19 tothe control circuit 5. In response to this signal, the control circuit 5calculates an amount of one injection, taking a signal from an enginespeed sensor 10 into account, and feeds a signal to an injection valvedrive portion 20 of the fuel injection valve 13. As a result, the fuelinjection valve 13 is opened to inject the fuel into a combustionchamber 7. The timing of injection of the fuel and the amount ofinjection (injection time) at this time are optimally determined by thecontrol circuit 5. A signal is fed from the control circuit 5 to anignition circuit 22 at an optimum timing, and a high voltage is producedby the ignition circuit 22, and is fed to an ignition plug 14, so thatthe ignition plug 14 produces a spark to ignite the fuel injected intothe combustion chamber 7. The pressure within the combustion chamber 7increases, and acts on a piston 9 to impart a rotational force to acrankshaft 16, and tires 18 a and 18 b are driven through a transmission15 and a differential gear 17, thus causing a vehicle to travel. Withrespect to the torque produced by an engine 6, the combustion pressurewithin the combustion chamber 7 is detected by a pressure sensor 8, andis fed to the control circuit 5, and is compared with the signal of theaccelerator pedal 19 intended by the driver. The result of thiscomparison is reflected on the next or subsequent fuel injection in thecylinder. An amount of the air in the engine 6 is measured by an airamount sensor, and the flow rate of the air is controlled by a throttlevalve. The air is also controlled by a swirl control valve 28, providedin an intake manifold 27, so that a suitable turbulence can be formed inthe cylinder. A valve lift of an intake valve 12 is controlled by avalve lift control device 11. Combustion gas is discharged from anexhaust valve 21.

The first embodiment of the present invention will now be described withreference to FIG. 2 which is a vertical cross-sectional view of thecombustion chamber. The fuel injection valve 13 and the ignition plug 14are provided at an auxiliary combustion chamber 23 formed at an enginehead 25. With respect to the positional relation between the fuelinjection valve 13 and the ignition plug 14, it is preferred that theignition plug 14 be disposed downstream of the spray emitted from thefuel injection valve 13. With this arrangement, a flame core produced bythe ignition plug 14 is liable to be spread by the spray to thecombustion chamber 7 and a cavity 24 formed in the piston 9. However, ifthe ignition plug 14 is disposed too close to the spray, the ignitionplug 14 gets wet with the spray, so that an incomplete ignition may becaused. Therefore, it is important to properly determine the abovepositional relation. By throttling an outlet portion 26 of the auxiliarycombustion chamber 23, the speed of injection or jetting-out of theflame core can be adjusted. In this case, if the throttling isexcessive, a pressure loss develops, so that the heat efficiency islowered.

FIG. 3 shows the relation between the air/fuel ratio A/F and the exhaustgas (HC, NOx). When the fuel injection timing is a crank angle of 90°,the peak value of NOx is obtained when A/F is nearly 16. Such a changein the amount of discharge of NOx tends to be seen in a uniform mixture.The reason is that when the fuel injection timing is a crank angle 90°or up to an intermediate stage of the intake stroke, the injection sprayspreads out over the entire area in the cylinder because of flows of theair within the cylinder which flows are caused by the movement of thepiston and the intake operation. As the injection timing defined by thecrank angle becomes greater, the air/fuel ratio, at which the peak valueof NOx is obtained, becomes larger. At the same time, the production ofNOx becomes gentle. Also, the amount of discharge of HC varies.Comparing the injection timing 90° with the injection timing 180°, theamount of HC at the injection timing 90° at A/F of nearly 15 is 3,800ppmC while the amount of HC at the injection timing 180° at A/F ofnearly 15 is 6,500 ppmC. The reason why the amount of HC thus differs atthe same air/fuel ratio is that the air/fuel ratio at the region wherethe combustion is effected is different. Namely, the air/fuel ratio atthe region where the combustion is actually effected at the injectiontiming 180° is smaller. Therefore, when the air/fuel ratio increases, acombustion failure (extinction or flame-out) occurs at the injectiontiming 90° at the smaller air/fuel ratio. The reason why the air/fuelratio, enabling a stable combustion (the amount of HC does notincrease), increases with the increase of the injection timing is thatthe increased fuel injection timing approaches the ignition timing, sothat the fuel becomes less liable to spread, thus providing thestratified mixture. By thus selecting the injection timing, the uniformmixture and the stratified mixture can be formed freely. Therefore, whenthe engine torque is small, the injection timing is increased to bebrought near to the ignition timing. As the torque increases, theinjection timing is decreased to bring the mixture close to a uniformone.

FIG. 4 shows a vertical cross-sectional view of a combustion chamber ofa second embodiment. In this embodiment, a fuel injection valve 13 isprojected into the combustion chamber 7, and an injection port is soformed that the fuel can spread widely within a cylinder. In this case,when the fuel is injected when a piston is lowered to a point near to abottom dead center, the fuel impinges directly on a wall surface of thecylinder to form a wall flow. In this condition, a good combustion cannot be expected. Therefore, where the injection valve injects a widespray, the fuel need to be injected at such a timing that a cavity 24 isdisposed near to an upper dead center, and that the fuel can be blowninto the cavity 24. For example, the injection of the fuel can beeffected a plurality of times in a divided manner, as shown in FIG. 5.An early injection is effected at a crank angle of nearly 0° to form auniform mixture. A combustion initiator is produced by a late injectioneffected at a timing near the ignition timing, and the uniform mixtureproduced by the early injection is rapidly burned thereby. The injectionamount can be adjusted by any of the late injection and the earlyinjection, and therefore the injection can be effected in the optimumcondition. In the case where the injection is thus divided into the twoinjections (that is, the early injection and the late injection), theeffect can be obtained also with the injection valve (FIG. 2) having asmall injection angle.

FIG. 6 shows a flow chart for calculation of the fuel injection time inthe case where the early injection and the late injection are effected.In Step 101, an accelerator opening degree α and an engine speed Ne areread. At this time, if the air amount is measured, the air amount Qa maybe also read. In Step 102, the fuel amount Qf is calculated. In Step103, Qf>Qf1 is judged. If the judgment result is “NO”, the programproceeds to Step 109 in which the injection time Tp2 is calculated byadding an invalid injection amount Qx to Qf. In Step 110, the fuel forTp2 is injected at the timing of the late injection, and the program isfinished. If the judgment result in Step 103 is “YES”, the programproceeds to Step 104 in which Qf2 is calculated by subtracting a minimuminjection amount Qf0 from Qf. In Step 105, the injection time Tp1 iscalculated by adding the invalid injection amount Qx to Qf2. The fuelfor Tp1 is injected at the timing of the early injection. In Step 107,Tp2 is calculated by adding Qx to Qf0, and the fuel for Tp2 is injectedat the timing of the late injection. Thus, for each of the early andlate injections, it is necessary to add the invalid injection amount Qx.

FIG. 7 shows a control system for controlling the fuel pressure. Fuelfor the fuel pump 2 is fed from the fuel tank 1. The fuel pump 2 isdriven by a motor 30, and the pressurized fuel is fed to a high-pressurepipe 34. Injection valves 13 a to 13 d, an accumulator 33, the fuelpressure sensor 3, and a relief valve 32 are mounted on thehigh-pressure pipe 34. Gas is sealed as a damper in the relief valve 33,and when the fuel pressure increases, the fuel flows into theaccumulator 33. When the pressure decreases, the accumulator 33discharges the fuel into the high-pressure pipe 34. When the fuelpressure becomes unduly high, the relief valve 32 allows the fuel toflow therethrough, thereby preventing the pressure increase. The fuelpressure sensor 3 feeds a signal, proportional to the pressure, to thecontrol circuit 5, and in response to this signal, the control circuit 5feeds a signal to the electromagnetic spill device 4 to control thedischarge amount of the fuel pump 2, thereby controlling the fuelpressure. Also, in response to the signal from the pressure sensor 3,the control circuit 5 feeds a signal to a controller 31 of the motor 30to control the rotational speed of the fuel pump 30, thereby controllingthe fuel pressure. In this embodiment, although the electromagneticspill device 4 and the controller 31 are both provided, the fuelpressure can be controlled by one of them. However, in the case wherethe fuel pump 2 is driven by the engine, only the electromagnetic spilldevice 4 is used for this purpose since the motor 30 is not provided.

FIG. 8 shows a control system diagram of EGR. The air enters the engine6 through an air flow meter 35, a throttle valve 37 and the intakemanifold 27, and is discharged as exhaust gas to exhaust pipe 41. Acatalyzer 39 is provided in the exhaust pipe 41. Here, when EGR becomesnecessary, the control device 5 feeds a signal to an EGR valve 38 toopen the same. The control device 5 also feeds a signal to a throttlevalve actuator 36 to close the throttle valve 37 to thereby reduce thepressure of the intake manifold 27 to a level lower than the atmosphericpressure. As a result, the exhaust gas flows from the exhaust pipe 41 tothe intake manifold 27 through the EGR valve 38 in proportion to thenegative pressure of the intake manifold. The rate of flow of theexhaust gas at this time is proportional to the negative pressure of theintake manifold, and therefore the pressure of the intake manifold isdetected by an intake manifold pressure sensor 40, and a signal is fedfrom this sensor 40 to the control device 5, and the degree of openingof the throttle valve 37 is adjusted by the throttle valve actuator 36.By controlling the degree of opening of the throttle valve 37, thepressure of the intake manifold 27 can be controlled, and the EGR amountcan be accurately controlled by a feedback control.

FIG. 9 shows a third embodiment of the present invention. The air iscontrolled by a throttle valve 213, and is drawn into an engine throughan intake manifold 214. A lift of an intake valve 208 can be changed byswitching cams 203 of different shapes. The switching of the cams 203 iseffected by switching rocker arms 210 by a hydraulic control valve 202.The hydraulic control valve 202 is operated, for example, by a solenoid.The degree of opening of the throttle valve 213 is controlled by a motor212. A sensor 220 for detecting a pressure within a cylinder is mountedon the engine. An injection valve 204 for injecting the fuel directlyinto the cylinder is mounted on the engine. A sensor 205 for detectingthe air/fuel ratio of exhaust gas is mounted on an exhaust pipe. Acatalyzer is also provided in the exhaust pipe. Preferably, thecatalyzer or catalyst is of a type which can remove NOx even when anexcessive amount of oxygen is present. Also, function of a three-waycatalyst, which can remove HC, CO and NOx at the same time under thecondition of a stoichiometric air/fuel ratio, is needed. Part of theexhaust gas is controlled by valves 215 and 218 which control the flowrate in the exhaust pipe. With this arrangement, the combustiontemperature is decreased, thereby reducing the amount of NOx. Thesecontrol valves are controlled by a control device 201. In order toreduce the fuel consumption, it is preferred that the pressure withinthe intake manifold be reduced to a level close to the atmosphericpressure, thereby reducing a pumping loss. For this purpose, thethrottle valve 213 is fully opened as much as possible. However, in thecase where the exhaust gas is recirculated through a pipe 216, it isnecessary that the pressure within the intake manifold should be lowerthan the pressure within the exhaust pipe, and therefore the throttlevalve is closed.

FIG. 10 shows the operation of the third embodiment of the presentinvention. According to the operating conditions, the lift of the intakevalve cam is changed, as shown in FIG. 10. When a large amount of theair is required, the lift of the intake valve is set as at A. When theamount of the air is small, the lift of the intake valve is changed intoa lift B or a lift C. By changing the lift, the overlap with an exhaustvalve is also changed. During a high-output or power operation, theperiod of overlap between the exhaust valve and the intake valve is madelonger. With this arrangement, the amount of the air can be changed bythe lift of the intake valve.

FIG. 11 shows one example of the construction of rocker arms 221, 223and 224 and cams 225, 226 and 227. The rocker arm 223 and the cam 225drive the intake valve for reciprocal movement. The rocker arm 226 andthe cam 224 are not fixed to each other, and are in a free condition.When switching the cams, the rocker arm 224 and the cam 226 drive theintake valve for reciprocal movement. The rocker arm 223 and the cam 225are not fixed to each other, and are in a free condition. With thisconstruction, the cams can be switched. In this example, although thelift of the cam is changed, the shape of the cam may be changed so as tocontrol the valve opening timing and the valve closing timing at thesame time.

FIG. 12 shows a map for selecting the cam in connection with the degreeof opening of an accelerator and the engine speed. In this example, thecam switching can be effected in a three-stage manner. When the enginespeed is low, with the accelerator opening degree kept low, a cam A fora small lift is selected. As the engine speed and the acceleratoropening degree increase, the cam is sequentially switched to thoseproviding a larger lift.

FIG. 13 shows a map for selecting the cam in connection with the enginetorque and the engine speed. In this example, the cam switching can beeffected in a three-stage manner. The engine torque has target torquevalues predetermined with respect to the accelerator opening degree.When the engine speed is low, with the engine torque kept small, a cam Afor a small lift is selected. As the engine speed and the engine torqueincrease, the cam is sequentially switched to those providing a largerlift.

FIG. 14 shows a method of controlling the amount of the intake air whenswitching the air/fuel ratio A/F. When the full-opening of the throttlevalve or the cam for a large lift is selected, the fuel amount increaseswith the decrease of the air/fuel ratio, so that the engine torque(output torque) increases. At the air/fuel ratio of around 16, theamount of discharge of NOx tends to increase, and therefore the air/fuelratio is skipped from 18 to 15. At this time, if the air/fuel ratio isswitched to 15, with the air amount kept intact, the amount of the fuelincreases, so that the engine torque increases as at C. This gives asense of difference or a feeling of physical disorder. Therefore, whenswitching the air/fuel ratio, the air amount is reduced to prevent theincrease of the fuel amount, and the engine torque is changed from A toB (FIG. 14), thereby reducing a shock. The air amount is adjusted by thethrottle valve or by switching the cam. If this is effected by thethrottle valve, the pressure within the intake manifold is decreased,thereby increasing the pumping loss. Therefore, preferably, this is doneby switching the cam as much as possible. Also, when the engine torquedecreases to such a level that the target engine torque is not achievedeven if the air/fuel ratio is not less than 70, the air amount isadjusted by the cam or the throttle valve.

FIG. 15 shows the relation between the amount of the fuel and the enginetorque (output torque). The engine torque can be increased by increasingthe fuel amount, and therefore the engine torque can be controlled bythe fuel amount.

FIG. 16 shows a fourth embodiment of the present invention. The amountQf of injection of fuel is determined by an engine condition detectionportion 301 (which detects the conditions of an engine such as anaccelerator opening degree α and an engine speed N) and a fuel injectionamount calculation portion 302 which calculates the amount Qf ofinjection of the fuel. In accordance with a charging efficiency map 303,the amount of the air of the engine is calculated at a portion 304, andthe air amount by each cam is determined, thus calculating the air/fuelratio. It is judged at a portion 305 whether or not the air/fuel ratiois within a combustible range. The cam is selected at a portion 306, andthe degree of opening of a throttle valve is determined at a portion307. If the air amount is excessive, the mixture becomes too lean, andtherefore the cam is switched to one providing a smaller lift. In theinjection within the cylinder, since the mixture within the cylinder isdirectly controlled, the limit of the lean mixture can be expanded ascompared with a conventional intake port injection system, and thereforethe range of the engine torque which can be controlled by the fuelamount is wider. Therefore, the engine torque can be controlled by thefuel amount without the need for finely controlling the air amount as inthe conventional system.

FIG. 17 shows a fifth embodiment of the present invention. Anaccelerator opening degree is detected by a detection means 311, and atarget torque is determined by a calculation means 312. An amount offuel is determined by a fuel amount calculation means 313 in accordancewith the target torque. If the air/fuel ratio is predetermined withrespect to the engine torque (output torque) T at a portion 314, the airamount Qa can be derived. The air/fuel ratio is judged by a judgmentmeans 316. If the air/fuel ratio is not less than 18, a throttle valveis fully opened, i.e. its opening degree θth→θmax, at a portion 318, andthe torque of the engine is detected by a torque detection means 319,and the fuel injection amount is controlled so that the target torquecan be obtained. On the other hand, if the air/fuel ratio is less than18, the air amount is controlled by the throttle valve 321 so that thetarget air/fuel ratio can be achieved. The air amount is controlled, forexample, by the throttle valve opening degree θth or the lift by a cam.Here, the air amount may be detected by an air amount sensor 322 tocontrol the air amount to a target value thereof.

FIG. 18 shows a map of the target air/fuel ratio. The air/fuel ratio isdecreased with the increase of the engine torque (output torque) T.However, at point B, the air/fuel ratio is switched to a point C in amanner to skip over the air/fuel ratio value 16. For further increasingthe torque, the air/fuel ratio is reduced toward a point D. If theair/fuel ratio is further reduced, the mixture becomes too rich.Therefore, preferably, at this region, the air amount is detected, andthe air/fuel ratio is controlled.

FIG. 19 shows the relation of the throttle valve opening degree θth withthe engine speed N and the intake air amount Qa. For controlling the airamount by the throttle valve, the throttle valve opening degree is foundfrom a map for the intake air amount. For effecting a more precise orfine control, the air amount is detected, and a feedback is effected.

FIGS. 20 and 21 shows a sixth embodiment of the present invention. Ifthe air/fuel ratio is not less than 18, the mixture is so lean that thedrivability and an exhaust cleaning effect may be lowered. Therefore, acombustion variation is detected, and a throttle valve opening degree ora cam lift are so set as to reduce the air amount.

FIG. 22 shows a seventh embodiment of the present invention. Anelectrode or terminal 234 is embedded in a cylinder gasket 231 of anengine, and a high voltage is applied thereto from an electrode orterminal 232. Screw holes 233 are formed in the gasket.

FIG. 23 is a vertical cross-sectional view of the portion of FIG. 22. Ahigh voltage is applied across electrodes 238 and 239 from an ignitioncoil, thereby producing a spark discharge. With this arrangement, themixture is ignited at a point near a cylinder wall surface and at otherpoints as well, so that the combustion speed increases. Moreover, sincethe combustion is started adjacent to the wall surface, a so-calledquench region near the wall surface is reduced, so that an amount ofunburned hydrocarbon is reduced, and also a knocking is less liable tooccur. Insulating layers 235 and 237 are provided on upper and lowersurfaces of the gasket, respectively. If the electrode 239 is an earthor ground electrode, the insulating layer 237 may be omitted.

An embodiment of the present invention will now be described withreference to FIG. 24. The amount of the intake air is measured by an airflow meter 501 mounted on an intake manifold. An engine speed isdetected by a crank angle sensor 509. In accordance with the amount ofthe intake air into a cylinder, as well as the engine speed, the amountof fuel is determined, and the fuel is injected into the cylinder by afuel injection valve 502. The air amount is controlled by a throttlevalve 551, connected to an accelerator wire, and a throttle valve 550controlled by a motor. The air amount may be controlled only by thethrottle valve 550; however, if the throttle valve 551 connected to theaccelerator wire is provided, the air amount will not become excessiveeven in the event of an abnormal operation of the throttle valve 550. Acatalyzer 506, which can oxidize CO and HC, and can reduce NOx in anoxidizing atmosphere, is provided at an exhaust pipe 512. Therefore,even if oxygen is present in the exhaust gas as in a lean combustion,NOx can be reduced. The air/fuel ratio is detected by an air/fuel ratiosensor connected to the exhaust pipe, and it is examined whether or nota target air/fuel ratio is achieved. If the air/fuel ratio is more leanthat the target value, the fuel amount is increased. HC is required forreducing NOx in an oxidizing atmosphere, and the temperature of thecatalyzer is so controlled that a maximum cleaning efficiency of thecatalyzer can be achieved. Therefore, the temperature of the catalyzeris detected by a temperature sensor 528, and the fuel injection amountand the ignition timing are so controlled that the target catalyzertemperature and HC can be obtained. A charging operation of a charger514 can be controlled from the outside by a control device 508. Thecharging operation is effected during a deceleration, thereby recoveringa deceleration energy. The amount of the intake air into the engine canbe increased by a supercharger 511. The operation of the catalyzer isalso influenced by the oxygen concentration in the exhaust gas, andtherefore an air introduction passageway 534 is provided at an inlet ofthe catalyzer, and the air amount is controlled by a control valve 534.The air may be supplied by an air pump 535. When the air amount isincreased, the catalyzer is cooled by the air, and therefore the air maybe used for controlling the temperature of the catalyzer.

FIG. 25 shows the relation between a required torque Tv and the enginetorque Te. The description will be given with respect to an example inwhich a transmission (gearbox) has a five-stage (five-speed) gear ratio.In a fully-opened condition of the throttle valve, the fuel amount ischanged. When the required torque Tv is small, a 5th speed (5th gear)with a small or low gear ratio is selected. When the required torque Tvbecomes larger, the fuel amount is increased to increase the enginetorque Te. At this time, in order to achieve a stable combustion, thefuel amount is within a lean combustion limit, and the air/fuel ratio isvaried in the range of 30 to 20 so that the amount of NOx can be keptsmall. However, in view of the cleaning or removing property of the NOxcatalyzer, the range of the air/fuel ratio may be changed. Also, if thestable combustion limit allows the air/fuel ratio to be furtherincreased, the air/fuel ratio may be more than 30. A pumping loss isreduced when the operation is effected with a large air/fuel ratio, andthe fuel consumption is enhanced. When the required torque Tv becomesfurther larger, the gear ratio is increased into a 4th speed. At thistime, if the gear is changed with the air/fuel ratio kept at 20, thedrive torque becomes excessive, so that a step develops in the torque,thereby adversely affecting the drivability. Therefore, the fuel amountis reduced to decrease the torque to be produced, thereby preventing astepwise change in the drive torque. Similarly, as the required torqueis increasing, the gear is sequentially changed. The drive torque can beobtained in the following:

(Drive torque)=(Engine torque)×(Gear ratio)

Namely, the larger the gear ratio becomes, the larger the drive torquebecomes. If the air/fuel ratio range of between 20 and 30 is fixedlyselected, the gear ratio is selected so that a torque step will notdevelop. Assuming that the air/fuel ratio is 20 at a 1st speed, when alarger torque than that is required, the air/fuel ratio is furtherdecreased. The required torque Tv is determined, for example, by thedegree of opening of an accelerator. When the accelerator opening degreeis large, the required torque Tv is large.

FIG. 26 shows the relation between the degree θ of opening of thethrottle valve and the required torque Tv. When the required torque Tvis small, the throttle valve opening degree θ is decreased to reduce theengine torque. When the required torque becomes larger, the throttlevalve opening degree θ is fully increased, and the gear ratio issequentially changed. At the 1st speed, the air/fuel ratio is skipped inview of the amount of production of NOx, so that a torque step develops.Therefore, the throttle valve opening is controlled in a closingdirection so as to minimize a torque step. The throttle valve openingdegree is controlled by a motor or the like. Since the control of thethrottle valve can be made only in the closing direction of the valve,the engine torque will not increase against the driver's will. It ispreferred that the throttle valve be fully opened, but if the operationcan be effected in the fully-opened condition because of the performanceof the engine, the operation is effected, with the throttle valve openedas much as possible.

FIG. 27 shows the relation between the required torque Tv and the gearposition V for the vehicle speed. The gear position V is changed inaccordance with the vehicle speed. The gear position V is increased withthe increase of the vehicle speed. When the gear position V isdecreased, the drive torque can be increased. The description will begiven with respect to an example in which the vehicle speed is increasedfrom a low speed, with the throttle valve fully opened. When the vehiclespeed increases from the 1st speed (1st gear) to the lower limit of the2nd speed, the air/fuel ratio is changed from 30 to 20, therebyminimizing or avoiding a torque step. As the required torque decreases,the air/fuel ratio is changed from 20 to 30. When the vehicle speedfurther increases, the gear is changed to the 3rd speed, and at thistime the air/fuel ratio is changed to 20, thereby avoiding a torquestep. A similar operation is repeated until the 5th speed. When therequired torque is to be changed at the 1st speed, the air/fuel ratio isbrought into 30 in the fully-opened condition of the throttle valve.When the torque need to be further increased, the fuel amount isincreased to change the air/fuel ratio to 20. When the torque is small,the throttle valve opening degree is reduced to decrease the air amount.When the air/fuel ratio is constant, the fuel amount decreases with thedecrease of the air amount, so that the torque is reduced. When therequired torque is small, but is larger than that of the lower limitvehicle speed of the 5th speed, the 5th speed is selected. When thevehicle speed is made lower than the lower limit vehicle speed of the5th speed, the engine speed becomes too low. When at the 5th speed inthe fully-opened condition, a larger torque is required than thatobtained with the air/fuel ratio of 20, the 4th speed is selected if thevehicle speed is higher than the lower limit of the 4th speed. At thistime, the air/fuel ratio is changed to 30, thereby avoiding a torquestep. When at the 4th speed in the fully-opened condition, the torque isto be made smaller than that obtained with the air/fuel ratio of 30, thethrottle valve is closed. Similarly, when the required torque is to beincreased, the gear is changed to the 3rd speed. The torque iscontrolled by sequentially changing the gear to the 1st speed in asimilar manner.

FIG. 28 shows the relation between the vehicle speed lower than thelower limit vehicle speed of the 1st speed and the engine torque Te atan outlet of a torque converter. Below the lower limit vehicle speed,when the transmission (gearbox) is kept in an engaged condition, theengine speed becomes too low, and in an extreme case, the engine isstopped. In such a speed region, a so-called lock-up (by which thetransmission and the engine are directly connected together) isreleased, and the transmission is connected to the engine through thetorque converter. When the vehicle speed decreases, there develops aslip region where there is a difference in rotational speed between theinlet and outlet of the torque converter. In the slip region, the torqueis increased, and the engine torque at the outlet of the torqueconverter is increased. The engine torque can be changed by the air/fuelratio. When the engine torque is, for example, not higher than 800 rpm,the lock-up is released. However, if the torque converter involves aslip, the torque converter produces a loss of transmission of theenergy, so that the fuel consumption is worsened.

FIG. 29 shows a flow chart of the control of the transmission and theengine. The engine speed is calculated from the accelerator openingdegree and the vehicle speed where number of gear shift positions r=5.When the engine speed is, for example, not more than 800 rpm, the gearposition is shifted down by one speed (one gear) so that the enginespeed will not be below 800 rpm. In the flow chart, although the gearposition is sequentially shifted down, the gear position may bedetermined in accordance with the minimum allowable engine speed and thevehicle speed. Tf the gear position is larger than the 1st speed (1stgear), the lock-up is effected. When the gear position is the 1st speed,the gear position can not be shifted down any further even if the enginespeed is lower than the minimum allowable engine speed, and thereforethe lock-up is released. After the gear position is determined, therequired engine torque (required torque) for the drive torque requiredby the driver is calculated. The fuel amount is calculated from therequired torque, and the air/fuel ratio when fully opening the throttlevalve is calculated. If the air/fuel ratio is not less than 30, thecombustion becomes unstable, and therefore the throttle valve openingdegree is so determined by calculation that the air/fuel ratio becomes30. The associated actuators (the fuel injection valve, the throttlevalve and the transmission) are so controlled that the fuel amount,throttle valve opening degree and gear position thus determined can beobtained. On the other hand, if the air/fuel ratio is not more than 20,the gear position is determined as (r−1), and the engine speed iscalculated again. At this time, the fuel amount is controlled not toproduce a drive torque step. Also, when the gear position is the 1stspeed (1st gear), the gear position can not be shifted down any further,and therefore the air/fuel ratio is changed from 12 to 15. Since theair/fuel ratio is skipped at this time so as to reduce the amount ofdischarge of NOx, the throttle valve opening degree is so determined bycalculation that a drive torque step will not develop, and the actuatorsare controlled.

FIG. 30 shows the relation between the accelerator opening degree andthe required drive torque. As the accelerator opening degree decreases,the required drive torque is decreased. At the same accelerator openingdegree, the required drive torque is decreased as the vehicle speedincreases. That the required torque can have a negative value means anengine brake. At the same accelerator opening degree, the higher thevehicle speed is, the more effectively the engine brake acts.

The required drive torque is determined for the accelerator openingdegree and the vehicle speed, as shown in FIG. 31. These values arestored as a map in a memory of a computer for control purposes. Forexample, the accelerator opening degree, as well as the vehicle speed,is divided into 16, and 256 values of the required drive torque arestored.

FIG. 32 shows the relation between the engine speed and the enginetorque. At the same engine speed, the larger the throttle valve openingdegree is, the larger the torque is. By controlling the throttle valveopening degree, the engine torque can be controlled. Also, since theengine torque varies depending on the air/fuel ratio, the torque iscontrolled by changing the throttle valve opening degree and the fuelamount.

As to other advantageous effects of the present invention, the amount ofthe intake air is larger when using supercharging than when not usingthe supercharging, and the engine torque increases as shown in FIG. 33.If an exhaust turbo charger is used as the supercharging means,regardless of the driver's will, the torque characteristics with thesupercharging are represented by a curve (a) while the torquecharacteristics without the supercharging are represented by a curve(b). Therefore, the engine output or power is abruptly increased wheneffecting the acceleration, and this gives a sense of difference or afeeling of physical disorder.

FIG. 34 is a time chart showing the change of the engine torque and thethrottle valve opening degree with time. When an accelerator pedal ispressed down, the amount of the air is increased, so that the fuelinjection amount is increased. When the supercharging is effected, theair amount is abruptly increased, the torque is increased as shown by(b) of FIG. 34 regardless of the driver's will, and this gives the senseof difference. When the supercharging is not effected, thetime-dependent change of the engine torque with respect to atime-dependent change of the throttle valve opening degree isrepresented by (a) in FIG. 34. Thus, a certain period of time isrequired because of the inertia force before the speed by thesupercharging becomes high, and therefore the supercharging becomeseffective halfway during the acceleration.

FIG. 35 shows a control block diagram according to another embodiment ofthe present invention. The acceleration of the vehicle body is detectedby an acceleration sensor, and if a desired drive torque is notobtained, the gear ratio (transmission ratio) of the engine is changed.

FIG. 36 shows the change of the fuel amount and the vehicle bodyacceleration with time. In order to determine the target accelerationfor the accelerator opening degree as shown in this Figure, the fuelamount is increased to increase the engine torque. In the injectionwithin a cylinder, the fuel can be injected directly into the cylinder,and therefore the fuel will not deposit on an intake manifold and thelike, and the torque can be controlled with a good response. Theacceleration is detected, and the fuel amount is so controlled that thetarget acceleration can be achieved.

FIG. 37 shows the change of the intake air amount, the fuel amount andthe vehicle body acceleration with time. In order to determine thetarget acceleration for the accelerator opening degree as shown in thisFigure, the fuel amount and the intake air amount are increased toincrease the engine torque. The intake air amount is controlled by thethrottle valve opening degree, but a delay occurs due to a volume of anintake manifold, so that the torque can not be controlled in a goodresponse. Therefore, a large change of the engine torque is controlledby the air amount, and the control for small variations is effected bythe fuel amount. In such a control, the range of change of the air/fuelratio can be narrowed, and also the engine torque can be controlled overa wide range.

In the present invention, since the throttle valve full-open region ismuch used, the engine brake is less liable to act effectively at thetime of the deceleration. Therefore, at the time of the deceleration,the electric charger is operated, thereby effecting an electric chargingcontrol. By doing so, the engine brake is achieved at the time of thedeceleration, and also the energy at the time of the deceleration can berecovered. With respect to the decelerated condition, for example, whenan injection pulse Tp is not greater than a predetermined value Tpc, thethrottle valve opening degree is not greater than a predetermined value,and the engine speed Ne is not less than a predetermined value, it isjudged that the deceleration occurs, and the electric charging operationis effected. Also, when the accelerator opening degree is not lower thana predetermined value, the charging operation is effected regardless ofwhether or not the injection pulse is below the predetermined value.During the charging operation, the charging target voltage is increasedto increase a charging load. Other load such as a fuel heater may beused as the charging load. When the throttle valve is used, the throttlevalve is closed during the deceleration.

In the present invention, the combustion time is shortened, the knockingis prevented, the compression ratio of the engine is increased, the heatefficiency is enhanced, and the fuel consumption is enhanced. Theproduction of unburned hydrocarbon can be prevented by the stratifiedintake. The response to the fuel is enhanced by the fuel injectionwithin the cylinder. Without increasing the pumping loss, the engineoutput or power can be controlled in a good response, thereby enhancingthe drivability.

What is claimed is:
 1. A method of controlling an internal combustionengine, into a combustion chamber of which fuel is injected, whereinwhen air/fuel ratio is lean, a throttle valve is fully opened and a fuelinjection amount is controlled so that a target torque can be obtained,and when the air/fuel ratio is rich or stoichiometric, an air amount iscontrolled so that a target air/fuel ratio can be achieved.
 2. A methodaccording to claim 1, wherein in said torque control, combustionvariation is detected and when the detected combustion variation islarger than a predetermined value, the air amount is reduced.
 3. Amethod according to claim 2, wherein said air amount control is effectedby controlling an opening degree of the throttle valve or a cam lift. 4.A method according to claim 1, wherein a lean fuel mixture is acondition in which the air/fuel ratio is not less than 18.